Geothermal In The Lesser Antilles
Emera Caribbean Inc. and Reykjavik Geothermal, in association with the Government of St. Vincent and the Grenadines, are planning a 10 MW geothermal power plant at the foot of La Soufriere on the northern part of St. Vincent.
By: Gestur Gislason, senior geochemist at Reykjavik Geothermal &
Snorri Gudbrandsson, PhD geochemist at Reykjavik Geothermal
Annually, about 140 GWh of electricity is produced to meet the needs of St. Vincent Electricity Services’ (VINLEC’s) customers. The planned 10 MW geothermal power plant has the potential to serve about 60% of the electricity needs of St. Vincent’s residents and businesses.
About geothermal around the world and in the Caribbean
Geothermal power plants have been built in 25 countries around the globe, with a total 12,635 MW installed capacity and an annual production of 73,549 GWh. Closer to home, the eastern boundary of the Caribbean geological structure is the Lesser Antilles Volcanic Arc, with its numerous volcanoes and related geothermal activities. The Volcanic Arc is located in the subduction zone were the Atlantic plate moves beneath the Caribbean Plate, forming the Lesser Antilles Volcanic Arc.
The heat source which keeps the geothermal systems active in geological settings in the Lesser Antilles is magma, which is formed more than 100 km deep under the Volcanic Arc. Only a small portion reaches the surface in an eruption, but the bulk of the magma settles as intrusions or in magma chambers above the location of formation (melting). Most of the intrusions are found at great depth, but magma chambers can reach up to 7 km in depth.
Drilling for geothermal steam
Geothermal is used either directly, providing energy for an array of uses such as space heating or cooling, in aquaculture and drying, or for electricity production. In St. Vincent, we are exploring the possibility of using geothermal steam for electricity production. For this purpose, temperatures above 200°C are necessary, which requires drilling through the cap rock. The depth of a geothermal well is most commonly 2-2.5 km deep.
Geothermal activity is a product of magmatic activity. As a consequence, most geothermal power stations are located in volcanic areas near lava and eruptive sites. Eruptions occur when lava, gases or ash escapes from a magma chamber below. Because geothermal wells are rarely deeper than 3.5 km and the magmatic heat source is generally below 7 km depth, direct contact, and therefore eruption, is unlikely.
Thousands of geothermal wells have been drilled into active geothermal reservoirs, and there has been no triggering of volcanic activity. Indonesia and the Philippines have subduction zones that are similar to St. Vincent. In Indonesia, which produces 1,340 MW of geothermal energy annually, and in the Philippines, at 1,870 MW annually, more than 600 5-MW geothermal boreholes have been drilled without triggering eruption.
There have been a small number of cases where a borehole has been drilled into a body of molten magma without causing any major problems, where the equipment was safely retrieved and no magma was ejected to the surface.